Eutectic Bonding With ALGe

ABSTRACT

A MEMS device formed in a first semiconductor substrate is sealed using a second semiconductor substrate. To achieve this, an Aluminum Germanium structure is formed above the first substrate, and a polysilicon layer is formed above the second substrate. The first substrate is covered with the second substrate so as to cause the polysilicon layer to contact the Aluminum Germanium structure. Thereafter, eutectic bonding is performed between the first and second substrates so as to cause the Aluminum Germanium structure to melt and form an AlGeSi sealant thereby to seal the MEMS device. Optionally, the Germanium Aluminum structure includes, in part, a layer of Germanium overlaying a layer of Aluminum.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims benefit under 35 USC 119(e) ofApplication Ser. No. 62/481,634, filed Apr. 4, 2017, the contents ofwhich is incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to wafer bonding, and more particularly toeutectic bonding for sealing MEMS devices.

BACKGROUND

Micro Electro-Mechanical Systems (MEMS), such as motion sensors andmovable mirrors, are being widely used. As is well known, a MEMS motionsensor may be, for example, an accelerometer for detecting linearmotion, or a gyroscope for detecting rotation and angular velocity.

Advanced planar silicon processes are being increasingly used tomanufacture MEMS devices. Glass frit bonding has been used forwafer-level packaging of MEMS devices, such as accelerometers. However,due to its limitation in achievable minimum seal width, cost, and leadcontent, a substantial number of the current generation of gyroscopesare made using other wafer-level packaging solutions, such as eutecticsolder bonding.

To be effective, a eutectic wafer bonding processes require cleansurfaces. Excessive amounts of native oxides and other organiccontaminants on the surfaces may damage surface bond formation,strength, and integrity. Depending on the materials in the seal layerstack and device configurations, the removal of the native oxide layerand other contaminants from the surface being bonded may causedifficulties. Robust wafer bonding and sealing of MEMS devices usingeutectic wafer bonding processes continues to pose challenges.

BRIEF SUMMARY OF THE INVENTION

A method of sealing a MEMS device formed in a first semiconductorsubstrate using a second semiconductor substrate, in accordance with oneembodiment of the present invention, includes, in part, forming anAluminum Germanium structure above the first substrate; forming apolysilicon layer above the second substrate; covering the firstsubstrate with the second substrate so as to cause the polysilicon layerto contact the Aluminum Germanium structure; and performing eutecticbonding between the first and second substrates so as to cause theAluminum Germanium structure to melt and form a AlGeSi sealant therebyto seal the MEMS device. In one embodiment, the Germanium Aluminumstructure comprises a layer of Germanium overlaying a layer of Aluminum.

In one embodiment, the method further includes, in part, forming anadhesive layer below the Aluminum Germanium structure in the firstsubstrate. In one embodiment, the method further includes, in part,forming an Alumina layer between the Aluminum Germanium structure andthe adhesive layer. In one embodiment the adhesive layer is a TitaniumNitride layer. In one embodiment, the method further includes, in part,forming an Alumina layer below the Polysilicon layer in the secondsubstrate. In one embodiment, the method further includes, in part,forming a Polycide layer below the Polysilicon layer in the secondsubstrate. In one embodiment, the method further includes, in part,forming an adhesive layer below the Alumina layer in the secondsubstrate.

A method of sealing a MEMS device formed in a first semiconductorsubstrate using a second semiconductor substrate, in accordance with oneembodiment of the present invention, includes, in part, forming aSilicide layer either in or above the first substrate; forming anAluminum Germanium structure above the Silicide layer of the firstsubstrate; forming a Silicide layer either in or above a substrate ofthe second substrate; covering the first substrate with the secondsubstrate so as to cause the Aluminum Germanium structure of the firstsubstrate to contact the Silicide layer of the second substrate; andperforming eutectic bonding between the first and second substrates soas to cause the Aluminum Germanium structure to melt and form a AlGeSisealant thereby to seal the MEMS device.

A method of sealing a MEMS device formed in a first semiconductorsubstrate using a second semiconductor substrate, in accordance with oneembodiment of the present invention, includes, in part, forming aSilicide layer either in or above the second substrate; forming anAluminum Germanium structure above the Silicide layer of the secondsubstrate; covering the first substrate with the second substrate so asto cause the Aluminum Germanium structure of the second substrate tocontact the Silicide layer of the first substrate; and performingeutectic bonding between the first and second substrates so as to causethe Aluminum Germanium structure to melt and form a AlGeSi sealantthereby to seal the MEMS device.

A method of sealing a MEMS device formed in a first semiconductorsubstrate using a second semiconductor substrate, in accordance with oneembodiment of the present invention, includes, in part, forming aSilicide layer either in or above a substrate of the first substrate;forming an Aluminum Germanium structure above the Silicide layer of thefirst substrate; forming a Silicide layer either in or above a substrateof the second substrate; forming an Aluminum Germanium structure abovethe Silicide layer of the second substrate; covering the first substratewith the second substrate so as to cause the Aluminum Germaniumstructure of the first substrate to contact the Aluminum Germaniumstructure of the first substrate; and performing eutectic bondingbetween the first and second substrates so as to cause the AluminumGermanium structure to melt and form a AlGeSi sealant thereby to sealthe MEMS device.

A method of sealing a MEMS device formed in a first semiconductorsubstrate using a second semiconductor substrate, in accordance with oneembodiment of the present invention, includes, in part, forming aSilicide layer either in or above a substrate of the first substrate;forming an Aluminum Germanium structure above the Silicide layer of thefirst substrate; forming a Silicide layer either in or above a substrateof the second substrate; forming an Aluminum structure above theSilicide layer of the second substrate; covering the first substratewith the second substrate so as to cause the Aluminum Germaniumstructure of the first substrate to contact the Aluminum structure ofthe second substrate; and performing eutectic bonding between the firstand second substrates so as to cause the Aluminum Germanium structure tomelt and form a AlGeSi sealant thereby to seal the MEMS device.

A method of sealing a MEMS device formed in a first semiconductorsubstrate using a second semiconductor substrate, in accordance with oneembodiment of the present invention, includes, in part, forming aSilicide layer either in or above a substrate of the first substrate;forming a Germanium structure above the Silicide layer of the firstsubstrate; forming a Silicide layer either in or above a substrate ofthe second substrate; forming an Aluminum Germanium structure above theSilicide layer of the second substrate; covering the first substratewith the second substrate so as to cause the Aluminum Germaniumstructure of the second substrate to contact the Germanium structure ofthe first substrate; and performing eutectic bonding between the firstand second substrates so as to cause the Aluminum Germanium structure tomelt and form a AlGeSi sealant thereby to seal the MEMS device.

A MEMS structure, in accordance with one embodiment of the presentinvention, includes, in part, a MEMS device formed in a cavity of afirst semiconductor substrate and sealed in an AlGeSi sealant. TheAlGeSi sealant is formed in response to eutectic bonding between anAluminum Germanium structure formed in the first substrate and apolysilicon layer formed in a second semiconductor substrate.

In one embodiment, the Germanium Aluminum structure further includes, inpart, a layer of Germanium overlaying a layer of Aluminum. In oneembodiment, the MEMS structure further includes, in part, an adhesivelayer below the Aluminum Germanium structure. In one embodiment, theMEMS structure further includes, in part, an Alumina layer disposedbetween the Aluminum Germanium structure and the adhesive layer. In oneembodiment, the adhesive layer is a Titanium Nitride layer. In oneembodiment, the MEMS structure further includes, in part, an Aluminalayer below the Polysilicon layer in the second substrate. In oneembodiment, the MEMS structure further includes, in part, a Polycidelayer below the Polysilicon layer in the second substrate. In oneembodiment, the MEMS structure further includes, in part, an adhesivelayer below the Alumina layer in the second substrate.

A MEMS structure, in accordance with one embodiment of the presentinvention, includes, in part, a MEMS device formed in a cavity of afirst semiconductor substrate and sealed in an AlGeSi sealant. TheAlGeSi sealant is formed in response to a eutectic bonding between anAluminum Germanium structure formed in the first substrate and aSilicide layer formed either in or above the second semiconductorsubstrate.

A MEMS structure, in accordance with one embodiment of the presentinvention, includes, in part, a MEMS device formed in a cavity of afirst semiconductor substrate and sealed in an AlGeSi sealant. TheAlGeSi sealant is formed in response to a eutectic bonding between anAluminum Germanium structure formed in a second semiconductor substrateand a Silicide layer formed either in or above the first semiconductorsubstrate.

A MEMS structure, in accordance with one embodiment of the presentinvention, includes, in part, a MEMS device formed in a cavity of afirst semiconductor substrate and sealed in an AlGeSi sealant. TheAlGeSi sealant is formed in response to a eutectic bonding between afirst Aluminum Germanium structure formed in the first semiconductorsubstrate, a second Aluminum Germanium structure formed in a secondsemiconductor substrate and a Silicide layer formed either in or abovethe first semiconductor substrate.

A MEMS structure, in accordance with one embodiment of the presentinvention, includes, in part, a MEMS device formed in a cavity of afirst semiconductor substrate and sealed in an AlGeSi sealant. TheAlGeSi sealant is formed in response to a eutectic bonding between afirst Aluminum Germanium structure formed in the first semiconductorsubstrate, a second Aluminum Germanium structure formed in a secondsemiconductor substrate and a Silicide layer formed either in or abovethe second semiconductor substrate.

A MEMS structure, in accordance with one embodiment of the presentinvention, includes, in part, a MEMS device formed in a cavity of afirst semiconductor substrate and sealed in an AlGeSi sealant. TheAlGeSi sealant is formed in response to a eutectic bonding between afirst Aluminum Germanium structure formed in the first semiconductorsubstrate, an Aluminum structure formed in a second semiconductorsubstrate, and a Silicide layer formed either in or above the firstsemiconductor substrate.

A MEMS structure, in accordance with one embodiment of the presentinvention, includes, in part, a MEMS device formed in a cavity of afirst semiconductor substrate and sealed in an AlGeSi sealant. TheAlGeSi sealant is formed in response to a eutectic bonding between afirst Aluminum Germanium structure formed in the first semiconductorsubstrate, an Aluminum structure formed in a second semiconductorsubstrate, and a Silicide layer formed either in or above the secondsemiconductor substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a device wafer following theformation of multiple layers thereon, in accordance with one exemplaryembodiment of the present invention.

FIG. 2A is a cross-sectional view of the device wafer of FIG. 1 after anumber of patterning and etching steps, in accordance with one exemplaryembodiment of the present invention.

FIG. 2B is a cross-sectional view of the device wafer of FIG. 1 after anumber of patterning and etching steps, in accordance with one exemplaryembodiment of the present invention.

FIGS. 3A and 3B respectively are cross-sectional and top views of thedevice wafer of FIG. 2A after the formation of a MEMS device in a cavityof the device wafer, in accordance with one exemplary embodiment of thepresent invention.

FIGS. 4A and 4B respectively are cross-sectional and top views of thedevice wafer of FIGS. 3A-3B following a number of patterning and etchingsteps to form an AlGe structure thereon, in accordance with oneexemplary embodiment of the present invention.

FIG. 5 is a cross-sectional view of a lid wafer adapted to cover thedevice wafer of FIGS. 4A-4B following the formation of multiple layersthereon, in accordance with one exemplary embodiment of the presentinvention.

FIGS. 6A and 6B respectively are cross-sectional and top views of thelid wafer of FIG. 5 following a number of patterning and etching steps,in accordance with one exemplary embodiment of the present invention.

FIG. 7A is a cross-sectional view of the lid wafer of FIG. 6A coveringthe device wafer of FIG. 4A, in accordance with one exemplary embodimentof the present invention.

FIG. 7B is a cross-sectional view of the lid wafer of FIG. 6A coveringthe device wafer of FIG. 4A, in accordance with another exemplaryembodiment of the present invention.

FIGS. 8A and 8B are simplified cross-sectional and top views of a devicewafer after it has been processed to include a MEMS device and aSilicide structure, in accordance with one exemplary embodiment of thepresent invention.

FIGS. 9A and 9B are cross-sectional and top views of the device wafer ofFIGS. 8A-8B, following a number of depositions, patterning and etchingsteps, in accordance with one exemplary embodiment of the presentinvention.

FIGS. 10A and 10B are cross-sectional and top views of a lid waferadapted to cover the device wafer of FIGS. 9A-9B following depositionand etching steps, in accordance with one exemplary embodiment of thepresent invention.

FIG. 11 is a cross-sectional view of the lid wafer of FIG. 10A coveringthe device wafer of FIG. 9A, in accordance with one exemplary embodimentof the present invention.

FIG. 12 is a simplified cross-sectional view of a device wafer after ithas been processed to include a MEMS device and a Silicide region, inaccordance with one exemplary embodiment of the present invention.

FIGS. 13A and 13B are cross-section and top views of the device wafer ofFIG. 12 after performing a number of processing steps to form anAluminum and Germanium structure thereon, in accordance with oneexemplary embodiment of the present invention.

FIG. 14 is a cross-sectional view of a lid wafer adapted to cover thedevice wafer of FIG. 13A, in accordance with one exemplary embodiment ofthe present invention.

FIG. 15 is a cross-sectional view of the lid wafer of FIG. 14 coveringthe device wafer of FIG. 13A, in accordance with one exemplaryembodiment of the present invention.

FIG. 16 is a cross-sectional view of a device wafer having a top surfacethat is covered by a lid wafer, in accordance with another exemplaryembodiment of the present invention.

FIG. 17 is a cross-sectional view of a device wafer having a top surfacethat is covered by a lid wafer, in accordance with another exemplaryembodiment of the present invention.

FIG. 18 is a cross-sectional view of a device wafer having a top surfacethat is covered by a lid wafer, in accordance with another exemplaryembodiment of the present invention.

FIG. 19 is a cross-sectional view of a device wafer having a top surfacethat is covered by a lid wafer, in accordance with another exemplaryembodiment of the present invention.

FIG. 20 is a simplified top layout view of a MEMS device, in accordancewith one exemplary embodiment of the present invention.

FIG. 21 provides a more detailed view of an area of the MEMS device ofFIG. 20, in accordance with one exemplary embodiment of the presentinvention.

FIGS. 22A and 22B provide more detailed views of a number of the layerswithin area identified FIG. 21, in accordance with one exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with one embodiment of the present invention, A MEMSdevice (alternatively referred to herein as sensor) is hermeticallysealed in a cavity by applying Aluminum-Germanium-Silicon (AlGeSi)eutectic wafer bonding between a first silicon wafer in which the MEMSdevice is formed (hereinafter referred to as device wafer) and a secondsilicon wafer (hereinafter referred to as lid wafer) covering the topsurface of the device wafer. To achieve this, the eutectic wafer bondingis adapted to enable a structure that includes Aluminum and/orGermanium, formed on either the device wafer, the lid wafer, or both, tobond with Silicon atoms present in a structure/region of either thedevice wafer, the lid wafer, or both, to form a strong AlGeSi sealantsealing/encasing the MEMS device. The processing steps for forming thedevice wafer and the lid wafer, in accordance with a number of exemplaryembodiments of the present invention, are described below.

FIG. 1 is a cross-sectional view of a device wafer (also referred toherein as substrate) 100 following the formation of multiple layersthereon, in accordance with one exemplary embodiment of the presentinvention. Device wafer 100 is shown as including, in part, an adhesionlayer 230, which may be a Titanium Nitride TiN layer having a thicknessranging, for example, from 100 nm to 200 nm. Device wafer 100 is alsoshown as including a layer 240 of Alumina (Al₂O₃), having a thicknessranging, for example, from 100 nm to 200 nm, and formed above adhesionlayer 230. Both TiN layer 230 and Alumina layer 240 may be depositedusing well known techniques, such as ALD, CVD or PVD processes.

Device wafer 100 is also shown as including an Aluminum layer 250overlaying Alumina layer 240, and a Germanium layer 260 overlayingAluminum layer 250. The thicknesses of Aluminum layer 250 and Germaniumlayer 260 are selected so as to enable eutectic bonding to take placewhen the required temperature and pressure are applied. For example,Aluminum layer 250 and Germanium layer 260 may be selected to havethicknesses of 980 nm and 530 nm, respectively.

Thereafter, using conventional patterning and etching processing steps,layers 230, 240, 250, and 260 are removed to form an opening 285 havingsidewalls 292, as shown in FIG. 2A.

The device structure shown in FIG. 2B is similar to the device structureshown in FIG. 2A except that in FIG. 2B, an opening 255 is formed inAlumina 240 to enhance electrical connection between Titanium Nitridelayer 230 undelaying Alumina layer 240, and Aluminum layer 250 andGermanium layer 260 overlaying Alumina layer 240.

Next, as shown in FIG. 3A, a cavity 110 is formed at opening 285 inSilicon substrate in which MEMS device 120 is formed using any one of anumber of conventional semiconductor processing techniques. FIG. 3B is atop view of device wafer 100 shown in FIG. 3A. It is understood thatcross-hatched region 300 in FIG. 3B corresponds to layers 230, 240, 250and 260 of FIG. 3A.

Thereafter, using conventional patterning and etching processes,Aluminum (Al) layer 250, and Germanium (Ge) layer 260 are etched to forman AlGe structure 280 around the periphery of cavity 110. FIGS. 4A and4B respectively are cross-sectional and top views of device wafer 100after the patterning and etching processes are carried out to form anAlGe structure 280.

FIG. 5 is a cross-sectional view of lid wafer 500 adapted to coverdevice wafer 100 to hermetically seal cavity 110 and device 120, inaccordance with one exemplary embodiment of the present invention. Lidwafer 500 is shown as including an adhesion layer 510, an Alumina layer520, and a Polysilicon layer 530. Adhesion layer 520 may includeTitanium nitride TiN, having a thickness ranging, for example, from 100nm to 200 nm. Alumina layer 520 may have a thickness ranging, forexample, from 20 nm to 100 nm. Polysilicon layer 530 may have athickness ranging, for example, from 100 nm to 150 nm. In oneembodiment, layer 520 may be a Polycide layer in place of an Aluminalayer. A Polycide layer may be a WSi layer, a MoSi layer, a CoSi layer,a NiSi layer, and the like.

To prepare lid wafer 500 as a cover for device wafer 100, usingconventional patterning and etching processes, layers 510, 520 and 530are etched to form a structure 580, as shown in FIG. 6A. The width W2 ofstep structure 580 may be greater than width W₁ of step structure 280shown in FIG. 4A. FIG. 6B is a top view of lid wafer 500 shown in FIG.6A.

To hermetically seal MEMS device 120, as seen from FIG. 7A, the topsurface of device wafer 100—shown in FIGS. 4A, 4B—is brought intocontact with the top surface of lid wafer 500—shown in FIGS. 6A and 6B.This is achieved by placing lid wafer 500 over device wafer 100 so as tobring step structures 280 and 580 into alignment. Alternatively, tohermetically seal MEMS device 120, device wafer 100 may be placed overlid wafer 500.

Thereafter, during a eutectic bonding when the required heat andpressure are applied, Aluminum and Germanium disposed in structure 280change their phases from solid to liquid to form an AlGe eutectic meltwhich subsequently reacts with the Silicon atoms present in thePolysilicon layer 530 to form a ternary AlGeSi. The AlGeSi so formedwets the undelaying Polycide or Alumina layer.

Incorporating Silicon atoms into the AlGe eutectic melt, in accordancewith embodiments of the present invention, increases the eutectic pointtemperature thus solidifying the melt while controlling and limiting itsflow. Alumina layer 240 provides a barrier against gas permeation andthe highly reactive eutectic melt. The Alumina also provides a suitableadhesion layer for the eutectic melt. In embodiments in which layer 240includes Polycide, the Polycide further acts as a barrier against theconduction diffusion and the highly reactive eutectic melt. The Silicidelayer reduces the reaction speed of the AlGe eutectic melt with thesilicon contained in the silicide layer. In other words, the rate ofsilicon incorporation into the liquid AlGe eutectic melt is made slowerto provide a more controlled transformation from an AlGe eutectic meltinto a tertiary AlGeSi. Any excessive uptake of Si and the resultingspike of Al or Ge into Silicon can be avoided or substantially reduced.A silicon layer (amorphous, polysilicon or any other type) on top of thesilicide layer can be used as an initial, easily accessible siliconsource for the AlGe eutectic melt to start the silicon incorporationinto the AlGe eutectic melt at a high rate, slowing down after the layeris completely dissolved. The silicide acts as a diffusion barrier toreduce the undesirablet diffusion of Al and Ge atoms away from theliquid eutectic melt into the layers below. The silicide layer furtheracts as an adhesion layer for the AlGe eutectic melt. A device substratetogether with a lid substrate sealing a MEMS device, in accordance withthe embodiments of the present invention, is alternatively referred toherein as a MEMS structure.

The device structure shown in FIG. 7B is similar to the device structureshown in FIG. 7A except that in FIG. 7B, an opening 255 is formed inAlumina 240 to enhance the electrical connection between adhesion layer230, which may be for example, Titanium Nitride TiN layer as describedabove or a Silicide layer as described further below, and Aluminum layer250 and Germanium layer 260 overlaying Alumina layer 240.

In accordance with one embodiment of the present invention, a Silicidelayer formed and patterned on the device wafer, the lid wafer, or both,provides the Silicon atoms for the AlGe eutectic melt, as describedfurther below. FIG. 8A is a simplified cross-sectional view of anexemplary device wafer 100 after it has been processed to include aSilicide step structure 610, as well as a MEMS device 120 in itsassociated cavity 110. FIG. 8B is a corresponding top view of devicewafer 100 showing Silicide step structure 610, cavity 110 and MEMSdevice 120.

To prepare device wafer 100 for sealing, an Aluminum layer 250 followedby a Germanium layer 260 are deposited on Silicide step structure 610.The Aluminum and Germanium layers 250, 260 are subsequently patternedand etched to form a structure 280. FIGS. 9A and 9B respectively arecross-sectional and top views of device wafer 100 after the patterningand etching processes are carried out to form structure 280.

FIG. 10A is a cross-sectional view of a lid wafer 700 adapted to coverdevice wafer 100 of FIG. 9B to hermetically seal cavity 110 and device120, in accordance with one exemplary embodiment of the presentinvention. To prepare lid wafer 700 as a cover for device wafer 100,using conventional patterning and etching processes, Silicide structure710 is formed on the surface of the lid wafer. FIG. 10B is acorresponding top view of device wafer 700 showing Silicide structure710 on its top surface.

As seen from FIG. 11, to hermetically seal MEMS device 120, the topsurface of device wafer 100—shown in FIGS. 9A, 9B—is brought intocontact with the top surface of lid wafer 700—shown in FIGS. 10A and10B. This is achieved by placing lid wafer 700 over device wafer 100 soas to bring Silicide structures 610 and 710 into alignment.Alternatively, to hermetically seal MEMS device 120, device wafer 100may be placed over lid wafer 700.

To seal MEMS device 100, during a eutectic bonding when the requiredheat and pressure are applied, Aluminum and Germanium in structure 280change their phases from solid to liquid to form an AlGe eutectic meltwhich subsequently reacts with the Silicon atoms present in Silicidestructures 610 and/or 710 to form a ternary AlGeSi. IncorporatingSilicon atoms into the AlGe eutectic melt, in accordance withembodiments of the present invention, increases the eutectic pointtemperature thus solidifying the melt and controlling/limiting its flow.

Although device wafer 100 of FIGS. 9A-9B is shown as including only aSilicide layer 610 disposed between the surface of its substrate andAluminum layer 250, it is understood that in other embodiments one ormore layers that include other materials (not shown) may be disposedbetween the surface of Silicon substrate 100 and Silicide structure 610.Furthermore, although device wafer 100 of FIGS. 9A-9B is shown asincluding only a single layer of Aluminum and Germanium, it isunderstood that in other embodiments (not shown), device wafer 100 mayinclude multiple layers of Aluminum and Germanium deposited thereon inan alternating manner. Moreover, although cover wafer 700 of FIGS.10A-10B is shown as including only a Silicide structure 710 above itssubstrate surface, it is understood that in other embodiments, one ormore layers that include other materials (not shown) may be disposedbetween the surface of the Silicon substrate 700 and Silicide structure710.

In accordance with another embodiment of the present invention, aSilicide region formed and patterned within the substrate of the devicewafer, the lid wafer, or both, provides the Silicon atoms for the AlGeeutectic melt, as described further below. FIG. 12 is a simplifiedcross-sectional view of a device wafer 100 after it has been processedto include a Silicide region 610, as well as a MEMS device 120 in itsassociated cavity 110.

To prepare device wafer 100 for sealing, layers of Aluminum andGermanium are deposited on Silicide region 610. The Aluminum andGermanium layers are subsequently patterned and etched to form astructure. FIGS. 13A and 13B respectively are cross-sectional and topviews of device wafer 100 after it has been processed, as describedabove, to include cavity 110, MEMS device 120, Silicide region 610 andstructure 280 that includes an Aluminum layer 250 and a Germanium layer260.

FIG. 14 is a cross-sectional view of an exemplary embodiment of a lidwafer 700 adapted to cover device wafer 100 of FIGS. 13A-13B tohermetically seal cavity 110 and device 120, in accordance with oneexemplary embodiment of the present invention. Lid wafer 700 is shown asincluding a Silicide region 710 formed in its substrate.

As seen from FIG. 15, to hermetically seal MEMS device 120, the topsurface of device wafer 100—shown in FIGS. 13A, 13B—is brought intocontact with the top surface of lid wafer 700—shown in FIG. 14. This isachieved by placing lid wafer 700 over device wafer 100 so as to bringSilicide regions 610 and 710 into alignment. Alternatively, tohermetically seal MEMS device 120, device wafer 100 may be placed overlid wafer 700.

To seal MEMS device 100, during a eutectic bonding when the requiredheat and pressure are applied, Aluminum and Germanium present instructure 280 change their phases from solid to liquid to form an AlGeeutectic melt which subsequently reacts with the Silicon atoms presentin the Silicide region 610 and/or 710 to form a ternary AlGeSi.Incorporating Silicon atoms into the AlGe eutectic melt, in accordancewith embodiments of the present invention, increases the eutectic pointtemperature thus solidifying the melt and controlling/limiting its flow.

Although device wafer 100 of FIGS. 13A, 13B is shown as including anAluminum layer 250 above Silicide region 610, it is understood that inother embodiments, one or more layers that include other materials (notshown) may be present between Aluminum layer 250 and Silicide region610. Furthermore, although device wafer 100 of FIGS. 13A and 13B isshown as including only a single layer of each Aluminum and Germanium,it is understood that in other embodiments (not shown), device wafer 100may include multiple layers of Aluminum and Germanium deposited thereonin an alternating manner. Furthermore, although in the embodiment shownin FIG. 14, lid wafer 700 is shown as including only a Silicide region710 formed in its substrate, it is understood that other embodiments oflid wafer 700 may include one or more layers disposed above Silicideregion 710.

FIG. 16 is a cross-sectional view of a device wafer 100 having a topsurface that is covered by lid wafer 700, in accordance with anotherexemplary embodiment of the present invention. The embodiment shown inFIG. 16 is similar to that shown in FIG. 15, except that in theembodiment of FIG. 16, structure 780 that includes an Aluminum layer 750and a Germanium layer 760 is formed over Silicide region 710 of lidwafer 700 and not on the device wafer 100. Device wafer 100 is shown asincluding a silicide region 610, as well as MEMS device 120 formed incavity 110.

To seal MEMS device 100, during a eutectic bonding when the requiredheat and pressure are applied, Aluminum and Germanium present instructure 280 change their phases from solid to liquid to form an AlGeeutectic melt which subsequently reacts with the Silicon atoms presentin the Silicide region 610 and/or 710 to form a ternary AlGeSi.Incorporating Silicon atoms into the AlGe eutectic melt, in accordancewith embodiments of the present invention, increases the eutectic pointtemperature thus solidifying the melt and controlling/limiting its flow.

Although lid wafer 700 of FIG. 16 is shown as including an Aluminumlayer 750 and a Germanium layer 760 above Silicide region 710, it isunderstood that in other embodiments, one or more layers that includeother materials (not shown) may be present between Aluminum layer 750and Silicide region 710. Furthermore, although lid wafer 700 of FIG. 16is shown as including only a single layer of each Aluminum andGermanium, it is understood that in other embodiments (not shown), lidwafer 700 may include multiple layers of Aluminum and Germaniumdeposited thereon in an alternating manner. Moreover, although in theembodiment shown in FIG. 16, device wafer 100 is shown as including onlya Silicide region 610 formed in its substrate, it is understood thatother embodiments of device wafer 100 may include one or more layersdisposed above Silicide region 610.

FIG. 17 is a cross-sectional view of a device wafer 100 having a topsurface that is covered by lid wafer 700, in accordance with anotherexemplary embodiment of the present invention. Device wafer 100 is shownas including an aluminum layer 250 as well as a Germanium layer 260 thatcollectively form an AlGe structure 280 disposed above silicide region610 of device wafer 100. Device wafer 100 is also shown as including, inpart, a MEMS device 120 formed in cavity 120. Lid wafer 700 is shown asincluding an aluminum layer 750 and a Germanium layer 760 thatcollectively form an AlGe structure 780 disposed above silicide region710 of lid wafer 700.

To seal MEMS device 100, during a eutectic bonding when the requiredheat and pressure are applied, Aluminum and Germanium change from solidto liquid so as to form an AlGe eutectic melt. The AlGe eutectic meltreacts with the Silicon atoms present in the Silicide region 610 and/orSilicide region 710 to form a ternary AlGeSi. Incorporating the Si atomsinto the AlGe eutectic melt, in accordance with embodiments of thepresent invention, increases the eutectic point temperature thussolidifying the melt while controlling and limiting its flow.

Although not shown in FIG. 17, it is understood that Silicide regions610 and 710 may be formed above their respective substrate surfaces, asshown for example, in FIG. 11. Furthermore, although not shown, one ormore layers of other materials may be disposed between Silicide region610 and Aluminum layer 250 of device wafer 100, and/or between theSilicide region 710 and Aluminum layer 750 of lid wafer 700.Furthermore, although the embodiment of FIG. 17 is shown as includingonly a single layer of each Aluminum and Germanium on each of the deviceand lid wafers, it is understood that in other embodiments (not shown),both the device and lid wafers may include multiple layers of Aluminumand Germanium deposited thereon in an alternating manner.

FIG. 18 is a cross-sectional view of a device wafer 100 having a topsurface that is covered by lid wafer 700, in accordance with yet anotherexemplary embodiment of the present invention. Device wafer 100 is shownas including an Aluminum layer 250 as well as a Germanium layer 260 thatare patterned and etched to collectively form an AlGe step structure 280disposed above silicide region 610 of device wafer 100. Device wafer 100is also shown as including, in part, a MEMS device 120 formed in cavity120. Lid wafer 700 is shown as including a Germanium layer 750 disposedabove silicide region 710 of lid wafer 700.

To seal MEMS device 100, during a eutectic bonding when the requiredheat and pressure are applied, Aluminum and Germanium change theirphases from solid to liquid to form an AlGe eutectic melt whichsubsequently reacts with the Silicon atoms present in the Silicideregion 610 and/or 710 to form a ternary AlGeSi. Incorporating the Siatoms into the AlGe eutectic melt, in accordance with embodiments of thepresent invention, increases the eutectic point temperature thussolidifying the melt while controlling and limiting its flow.

Although not shown in FIG. 17, it is understood that Silicide regions610 and 710 may be formed above their respective substrate surfaces, asshown for example, in FIG. 11. Furthermore, although not shown, one ormore layers of other materials may be disposed between Silicide region610 and Aluminum layer 250 of device wafer 100, and/or between theSilicide region 710 and Germanium layer 750 of lid wafer 700.Furthermore, although the embodiment of FIG. 17 is shown as includingonly a single layer each of Aluminum and Germanium on each of the deviceand lid wafers, it is understood that in other embodiments (not shown),both the device and lid wafers may include multiple layers of Aluminumand Germanium deposited thereon in an alternating manner.

FIG. 19 is a cross-sectional view of a device wafer 100 having a topsurface that is covered by lid wafer 700, in accordance with anotherexemplary embodiment of the present invention. Device wafer 100 is shownas including a Germanium layer 260 formed above its Silicide region 610.Device wafer 100 is also shown as including, in part, a MEMS device 120formed in cavity 120. Lid wafer 700 is shown as including an aluminumlayer 750 as well as a Germanium layer 760 that are patterned and etchedto collectively form an AlGe structure 780 disposed above Silicideregion 710 of lid wafer 700.

To seal MEMS device 100, during a eutectic bonding when the requiredheat and pressure are applied, Aluminum and Germanium change theirphases from solid to liquid to form an AlGe eutectic melt whichsubsequently reacts with the Silicon atoms present in the Silicideregion 610 and/or 710 to form a ternary AlGeSi. Incorporating the Siatoms into the AlGe eutectic melt, in accordance with embodiments of thepresent invention, increases the eutectic point temperature thussolidifying the melt while controlling and limiting its flow.

Although not shown in FIG. 19, it is understood that Silicide regions610 and 710 may be formed above their respective substrate surfaces, asshown for example, in FIG. 11. Furthermore, although not shown, one ormore layers of other materials may be disposed between Silicide region610 and Germanium structure 260 of device wafer 100, and/or between theSilicide region 710 and Aluminum layer 750 of lid wafer 700.Furthermore, although the embodiment of FIG. 19 is shown as includingonly a single layer each of Aluminum and Germanium on lid wafer 700, itis understood that in other embodiments (not shown), the lid wafer mayinclude multiple layers of Aluminum and Germanium deposited thereon inan alternating manner.

FIG. 20 is a simplified top layout view of a MEMS device 800, inaccordance with one exemplary embodiment of the present invention.Disposed near the center of MEMS 800 are drive masses 810. Formed alongthe periphery of the device is a Silicide layer 810. Positioned abovethe Silicide layer is the Aluminum Germanium stack layer 830. Also shownare a multitude of routing interconnects 830 formed from, for example,TiN/Al/TiN stack layer 840. Also shown in FIG. 20 is area 870 withinwhich two regions, namely 850 and 870 of TiN/Al/TiN are identified. TheAlumina layer (not shown in these Figures) in these two regions haveopenings to provide electrical connection between undelaying Silicidelayer 230 and overlaying Aluminum Germanium stack layer 830.

FIG. 21 provides a more detailed view of the structure shown in region860 of FIG. 20. Region 860 is shown as including a Silicide layer 820,an Aluminum Germanium stack layer 830 and a TiN/Al/TiN stack routinglayer 840. Region 870 is shown as including a circular TiN/Al/TiN stacklayer 840. FIG. 22A provides a more detailed view of region 860 showingopening 845 formed in the Alumina layer. For simplicity, AluminumGermanium stack layer 830 and the Alumina layer are not shown in FIG.22A. Also shown in FIG. 22A are Tungsten via plugs with TiN liner 855.FIG. 22B provides a more detailed view of region 870 showing opening 845formed in the Alumina layer. For simplicity, Aluminum Germanium stacklayer 830 and the Alumina layer are not shown in FIG. 22B. Also shown inFIG. 22B are Tungsten via plugs with TiN liner 855.

The above embodiments of the present invention are illustrative and notlimitative. Embodiments of the present invention are not limited by thetype of MEMS device. Embodiments of the present invention are notlimited by the type of deposition, patterning, etching, and othersemiconductor processing steps required to form the various layers andstructures described herein. Embodiments of the present invention arenot limited to any specific thicknesses of the layers described herein.Embodiments of the present invention are not limited to thematerials/layers described above. Accordingly, it is understood thatother semiconductor materials may be present between the various layersdescribed above. Other additions, subtractions or modifications areobvious in view of the present disclosure and are intended to fallwithin the scope of the appended claims.

What is claimed is:
 1. A method of sealing a MEMS device formed in afirst semiconductor substrate using a second semiconductor substrate,the method comprising: forming an Aluminum Germanium structure above thefirst substrate; forming a polysilicon layer above the second substrate;covering the first substrate with the second substrate so as to causethe polysilicon layer to contact the Aluminum Germanium structure; andperforming eutectic bonding between the first and second substrates soas to cause the Aluminum Germanium structure to melt and form a AlGeSisealant thereby to seal the MEMS device.
 2. The method of claim 1wherein said Germanium Aluminum structure comprises a layer of Germaniumoverlaying a layer of Aluminum.
 3. The method of claim 1 furthercomprising: forming an adhesive layer below the Aluminum Germaniumstructure in the first substrate.
 4. The method of claim 3 furthercomprising: forming an Alumina layer between the Aluminum Germaniumstructure and the adhesive layer.
 5. The method of claim 3 wherein saidadhesive layer is a Titanium Nitride layer.
 6. The method of claim 1further comprising: forming an Alumina layer below the Polysilicon layerin the second substrate.
 7. The method of claim 1 further comprising:forming a Polycide layer below the Polysilicon layer in the secondsubstrate.
 8. The method of claim 6 further comprising: forming anadhesive layer below the Alumina layer in the second substrate.
 9. Amethod of sealing a MEMS device formed in a first semiconductorsubstrate using a second semiconductor substrate, the method comprising:forming a Silicide layer either in or above the first substrate; formingan Aluminum Germanium structure above the Silicide layer of the firstsubstrate; forming a Silicide layer either in or above a substrate ofthe second substrate; covering the first substrate with the secondsubstrate so as to cause the Aluminum Germanium structure of the firstsubstrate to contact the Silicide layer of the second substrate; andperforming eutectic bonding between the first and second substrates soas to cause the Aluminum Germanium structure to melt and form a AlGeSisealant thereby to seal the MEMS device.
 10. The method of claim 1wherein said Aluminum Germanium structure comprises a layer of Germaniumoverlaying a layer of Aluminum, wherein said Aluminum layer comprisesCopper atoms.
 11. The method of claim 1 wherein said Aluminum Germaniumstructure comprises a layer of Aluminum and Germanium that areco-deposited.
 12. A method of sealing a MEMS device formed in a firstsemiconductor substrate using a second semiconductor substrate, themethod comprising: forming a Silicide layer either in or above the firstsubstrate; forming a Silicide layer either in or above the secondsubstrate; forming an Aluminum Germanium structure above the Silicidelayer of the second substrate; covering the first substrate with thesecond substrate so as to cause the Aluminum Germanium structure of thesecond substrate to contact the Silicide layer of the first substrate;and performing eutectic bonding between the first and second substratesso as to cause the Aluminum Germanium structure to melt and form aAlGeSi sealant thereby to seal the MEMS device.
 13. A method of sealinga MEMS device formed in a first semiconductor substrate using a secondsemiconductor substrate, the method comprising: forming a Silicide layereither in or above a substrate of the first substrate; forming anAluminum Germanium structure above the Silicide layer of the firstsubstrate; forming a Silicide layer either in or above a substrate ofthe second substrate; forming an Aluminum Germanium structure above theSilicide layer of the second substrate; covering the first substratewith the second substrate so as to cause the Aluminum Germaniumstructure of the first substrate to contact the Aluminum Germaniumstructure of the first substrate; and performing eutectic bondingbetween the first and second substrates so as to cause the AluminumGermanium structure to melt and form a AlGeSi sealant thereby to sealthe MEMS device.
 14. A method of sealing a MEMS device formed in a firstsemiconductor substrate using a second semiconductor substrate, themethod comprising: forming a Silicide layer either in or above asubstrate of the first substrate; forming an Aluminum Germaniumstructure above the Silicide layer of the first substrate; forming aSilicide layer either in or above a substrate of the second substrate;forming an Aluminum structure above the Silicide layer of the secondsubstrate; covering the first substrate with the second substrate so asto cause the Aluminum Germanium structure of the first substrate tocontact the Aluminum structure of the second substrate; and performingeutectic bonding between the first and second substrates so as to causethe Aluminum Germanium structure to melt and form a AlGeSi sealantthereby to seal the MEMS device.
 15. A method of sealing a MEMS deviceformed in a first semiconductor substrate using a second semiconductorsubstrate, the method comprising: forming a Silicide layer either in orabove a substrate of the first substrate; forming a Germanium structureabove the Silicide layer of the first substrate; forming a Silicidelayer either in or above a substrate of the second substrate; forming anAluminum Germanium structure above the Silicide layer of the secondsubstrate; covering the first substrate with the second substrate so asto cause the Aluminum Germanium structure of the second substrate tocontact the Germanium structure of the first substrate; and performingeutectic bonding between the first and second substrates so as to causethe Aluminum Germanium structure to melt and form a AlGeSi sealantthereby to seal the MEMS device.
 16. A MEMS structure comprising a MEMSdevice formed in a cavity of a first semiconductor substrate, the MEMSdevice being sealed in an AlGeSi sealant, said AlGeSi sealant formed inresponse to eutectic bonding between an Aluminum Germanium structureformed in the first substrate and a polysilicon layer formed in a secondsubstrate.
 17. The MEMS structure of claim 16 wherein said GermaniumAluminum structure comprises a layer of Germanium overlaying a layer ofAluminum.
 18. The MEMS structure of claim 16 wherein said MEMS structurefurther comprises an adhesive layer below the Aluminum Germaniumstructure.
 19. The MEMS structure of claim 18 wherein said MEMSstructure further comprises an Alumina layer disposed between theAluminum Germanium structure and the adhesive layer.
 20. The MEMSstructure of claim 19 wherein said adhesive layer is a Titanium Nitridelayer
 21. The MEMS structure of claim 16 wherein said MEMS structurefurther comprises an Alumina layer below the Polysilicon layer in thesecond substrate.
 22. The MEMS structure of claim 16 wherein said MEMSstructure further comprises a Polycide layer below the Polysilicon layerin the second substrate.
 23. The MEMS structure of claim 16 wherein saidMEMS structure further comprises an adhesive layer below the Aluminalayer in the second substrate.
 24. A MEMS structure comprising a MEMSdevice formed in a cavity of a first semiconductor substrate, the MEMSdevice being sealed in an AlGeSi sealant, said AlGeSi sealant formed inresponse to a eutectic bonding between an Aluminum Germanium structureformed in the first substrate and a Silicide layer formed either in orabove the second semiconductor substrate.
 25. A MEMS structurecomprising a MEMS device formed in a cavity of a first semiconductorsubstrate, the MEMS device being sealed in an AlGeSi sealant, saidAlGeSi sealant formed in response to a eutectic bonding between anAluminum Germanium structure formed in a second semiconductor substrateand a Silicide layer formed either in or above the first semiconductorsubstrate.
 26. A MEMS structure comprising a MEMS device formed in acavity of a first semiconductor substrate, the MEMS device being sealedin an AlGeSi sealant, said AlGeSi sealant formed in response to aeutectic bonding between a first Aluminum Germanium structure formed inthe first semiconductor substrate, a second Aluminum Germanium structureformed in a second semiconductor substrate and a Silicide layer formedeither in or above the first semiconductor substrate.
 27. A MEMSstructure comprising a MEMS device formed in a cavity of a firstsemiconductor substrate, the MEMS device being sealed in an AlGeSisealant, said AlGeSi sealant formed in response to a eutectic bondingbetween a first Aluminum Germanium structure formed in the firstsemiconductor substrate, a second Aluminum Germanium structure formed ina second semiconductor substrate and a Silicide layer formed either inor above the second semiconductor substrate.
 28. A MEMS structurecomprising a MEMS device formed in a cavity of a first semiconductorsubstrate, the MEMS device being sealed in an AlGeSi sealant, saidAlGeSi sealant formed in response to a eutectic bonding between a firstAluminum Germanium structure formed in the first semiconductorsubstrate, an Aluminum structure formed in a second semiconductorsubstrate, and a Silicide layer formed either in or above the firstsemiconductor substrate.
 29. A MEMS structure comprising a MEMS deviceformed in a cavity of a first semiconductor substrate, the MEMS devicebeing sealed in an AlGeSi sealant, said AlGeSi sealant formed by aeutectic bonding between a first Aluminum Germanium structure formed inthe first semiconductor substrate, an Aluminum structure formed in asecond semiconductor substrate, and a Silicide layer formed either in orabove the second semiconductor substrate.